1. Technical Field of the Invention
The present invention generally concerns electronic circuits in the area of radiofrequency/high frequency RF/HF electronics, in particular those adapted to applications for the public at large in a mobile communications system and/or to metrology applications. More precisely, the invention concerns noise measurement in these electronic circuits, in particular the phase noise of at least one oscillating and/or resonant device included in one of the circuits and whose oscillation and/or resonance frequency remains to be determined.
2. Description of Related Art
At the present time, the development of communications systems leads to developments in the electronic circuits used entailing a certain number of requirements, in particular in terms of integration, cost and reliability. The major difficulty regarding these requirements lies in the predicted behavior of these types of electronic circuits, notably when confronted with the increase in frequencies used which renders testing means even more complex.
This behavior concerns a first set of characteristics of these circuit types in relation to a second set of characteristics. The first set comprises the lifetime of the electronic circuit, its capability for faster frequencies, its accuracy, its versatility and more generally its various performance levels. The second set of characteristics comprises the stresses undergone by this type of circuit generally due to ambient temperature, external vibrations, electromagnetic surroundings of these circuits and hence the disturbances generated by this environment.
For the modeling of this behavior one particular measuring technique is usually used. It consists firstly of producing circuit prototypes, then of conducting a series of measurements of these prototypes to extract their performance curves. Then, in relation to these measurement results, the second step is to adjust various parameters of the circuits in order to draw close to desired performance levels. The preceding steps are repeated until an electronic circuit is finally obtained which offers the desired optimal performance. It is therefore necessary to measure the characteristics of the electronic circuit as regularly as possible to determine initial performance levels, and to monitor their development within an application.
One of the most important measurements in an electronic circuit, of interest to designers, is the measurement of its different noises, allowing translation of the influence exerted by the different stresses, and hence prediction of how the circuit will perform.
In a circuit comprising at least one oscillating and/or resonant device, particular attention is paid to measurement of a particular type of noise of the oscillating and/or resonant device: phase noise. This phase noise is effectively a limiting factor for a frequency increase and/or bit rate increase in mobile communications systems. By measurement of phase noise of an oscillating device it is meant phase or frequency fluctuations around the central frequency of this device. By measurement of residual phase noise in a resonant device it is meant the phase fluctuations of a signal passing through the resonant device between its input and its output.
The measurement of this phase noise signal, and indeed the measurement of any other parameter, can only be carried out if, right from the design stage of the electronic circuit, additional connection lines are provided so that it is possible to access directly the circuit element to be measured, so that it can be connected to an outside measuring instrument via a conventional measuring system. With the high frequencies of mobile communication systems, these additional connection lines are comparable to transmission lines which may insert dispersions in the measured signal. Said dispersions are also present in the main functioning of the electronic circuit, even if the measurement is inactive. Additionally said measuring system with all its component instruments is very voluminous and of high cost.
There is a need to overcome these disadvantages by proposing a considerable decrease in the size of the additional connection line of the electronic circuit, by reducing the size of the phase noise measuring device and positioning it as close as possible to the circuit.